what is particulate matter

Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. These particles can be so small that they can only be detected using an electron microscope. PM can come from many sources, including natural sources such as dust storms and forest fires, and human activities such as burning fossil fuels and biomass. PM can have harmful effects on human health, including heart disease, lung disease, and premature death. The International Agency for Research on Cancer (IARC) and the World Health Organization (WHO) have designated airborne particulates as a Group 1 carcinogen. PM is regulated by the National Ambient Air Quality Standards (NAAQS) in the United States. The EPA regulates two sizes of PM, PM10 and PM2.5, with PM2.5 being the most harmful to human health. PM can also affect the environment by reducing visibility, altering plant growth and yield, and soiling materials. Indoor activities such as smoking tobacco can also generate PM.